(1) Field of the Invention
The present invention relates to ejecting liquid polymers into the boundary layer of the fluid surrounding an underwater vehicle, and deals more specifically with a system for delivering pressurized polymer from a unique reservoir within the vehicle.
(2) Description of the Prior Art
Systems for storing and ejecting polymers into the boundary layer of an underwater vehicle are known. Generally speaking, such systems provide for a rigid storage tank in the vehicle, and suitable internal piping for ejecting liquid polymer into the fluid moving over the vehicle nose portion to provide a more laminar flow of the fluid through which the underwater vehicle is traveling.
One example of a typical prior art system can be found in U.S. Pat. No. 3,286,674 issued to Thompson, et al. In the disclosure of the Thompson, et al. patent, a pump is provided to pressurize sea water drawn through an inlet at the aft end of the vehicle and mixed with the polymer so the mixture is available for ejection at the nose of the vehicle to thereby reduce the tendency of the fluid flow around the vehicle to separate and/or become turbulent, the polymer and sea water mixture providing for a more laminar flow of the fluid mixture along the external surface of the underwater vehicle.
A similar system is disclosed in Hulsebos, et al., U.S. Pat. No. 3,392,693, and also in U.S. Pat. No. 4,186,679 issued to Fabula, et al.
These prior art systems teach the necessity for pressurizing a mixing chamber which is of rigid geometry and therefore occupies a substantial portion of the interior of the vehicle. Further, these prior art systems are not acoustically quiet enough to satisfy current requirements for underwater vehicles of the type used by the United States Navy for example. Air pockets trapped in such prior art systems, where the pressure is rapidly decreasing, create popping sounds that result in undesirable noise that can lead to premature detection of the vehicle in a combat situation.
The present invention also satisfies a need for meeting the requirements for an underwater vehicle in a testing environment where the vehicle is purposely made buoyant and is tested in a vertical ascent situation such that the fluid pressure at some depth is utilized to create the pressure required for ejecting the polymer and thereby reducing its drag as it travels to the surface of the water. In such tests, the buoyant vehicle is pulled downwardly underwater and the water enters a cavity defined within the vehicle, the entrapped air being vented overboard through a suitable vent in the vehicle's hull or shell. Even in such testing scenarios it is important to reduce the popping noises created by any air trapped within the system during ascent of the vehicle from its launch position well below the surface of the water.